Fox News host Chris Wallace forced Marco Rubio into a tight spot on immigration Sunday, asking the Florida Republican why he flip-flopped on his support for amnesty — sending the senator into a convoluted explanation when Wallace refused to let up.

Rubio appeared on “Fox News Sunday” to address the chances of comprehensive immigration reform in the wake of a growing border crisis. But he seemed unprepared for Wallace’s questions regarding his own evolution on the problem.

“You were one of the leaders for comprehensive immigration reform, for pushing it through the Senate, last year,” Wallace noted. “Yes, you dealt with border enforcement. But also at the same time you put in place a plan — an eventual, over the course of 12 to 15 years, a path to citizenship.”

The Fox News host noted that Rubio’s presidential polling took a nose dive after his plan became public. “Is that why you have now switched and said we have to do this in stages,” he asked. “With enforcement first and any dealing with legality or citizenship for the immigrants way down the line afterwards.”

“When I got involved in this issue I knew how difficult it was politically,” Rubio began. “But I ran for office to make a difference . . . I don’t know what it means politically for me or anybody else, but that’s not my job.”

“I didn’t get elected to maintain good poll numbers nationally,” he continued. “I got elected to address and solve problems.”

“But sir, if it’s not — if I may sir,” Wallace asked, as Rubio kept speaking. “If it’s not political, why have you flipped?”

“That’s not accurate, Chris,” Rubio retorted.

“But you’re now saying it has to be done in stages, before you wanted a comprehensive plan,” Wallace pressed.

The senator eventually explained that the three things he wants to see done on immigration — “security reform, modernizing the legal system and then address the people here” — will only be politically possible if done piecemeal.

“I’m just telling you, you’ll never have the votes necessary to pass, in one bill, all of those things,” Rubio concluded. “It just won’t happen.”